This invention relates generally to automatic control of machines for grinding. In particular, this invention relates to apparatus for automatically modifying the feed portion of a grinding or abrading machine cycle of operation to reduce deviations of finished part size from desired size without resort to in-process gaging.
It is known that part size deviation from desired size in nongage grinding is dependent on relative forces between the abrading wheel and the workpiece during the infeed portion of the grinding cycle. Although grinding cycles typically include a dwell period at the end of the infeed portion of the cycle, the resultant relief of relative forces between the abrading wheel and the workpiece does not insure that the workpiece finish size shall conform to the desired size. When the grinding wheel is new and relatively sharp, that is, the interstices of the abrading surface are open and the surrounding ridges are well defined, the wheel cuts the workpiece with less relative force than when the wheel is dull. Further, as the wheel wears and is reduced in diameter, the smaller diameter results in a smaller contact area and hence, less relative force between the wheel and the workpiece. As the cutting forces vary throughout the useful life of the cutting wheel, the rate of wheel wear also varys. Heretofore, it has been known to automatically compensate the feed portion of the grinding machine cycle to reflect a reduction of grinding wheel diameter with wear. However, this single compensation is not sufficient to adequately accomodate the effect of grinding force variation over the life of a wheel from its initial condition as a new wheel to the end of its useful life when its diameter is so reduced as to make continued use thereof impractical.
It is therefore, one object of the present invention to provide a control for a grinding machine having automatic compensating circuitry for modifying the infeed portion of a grinding cycle of operation to reduce deviations of final part size occurring over a plurality of workpieces and associated with changing conditions of the grinding wheel.
It is a further object of the present invention to provide a grinding machine infeed control having circuitry for producing a multifunction correction value to modify the infeed portion of the cycle to accomodate final size deviations occurring over a plurality of workpieces and attributable to a plurality of factors associated with changing conditions of the grinding wheel.
It is a still further object of the present invention to provide a grinding machine infeed control having circuitry for applying a first size correction value to a limited number of infeed cycles executed immediately following a grinding wheel sharpening operation and having circuitry for applying a second size correction value to all infeed cycles executed between sharpening operations.
A still further object of the present invention is to provide a grinding machine infeed control having zero shifting circuitry for modifying the final size detection point of the infeed cycle in accordance with two functions, a first function producing an offset value decreasing towards zero with each infeed cycle completion after an initialization and a second function producing an offset value increasing with each infeed cycle completion after the initialization.
Further objects and advantages of the present invention shall become apparent from the drawings and associated description.